1. Field of the Invention
The present invention relates generally to drills, and in particular, to a percussive augmenter of rotary drills (PARoD) for operating as a rotary-hammer drill.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by citations enclosed in brackets, e.g., [x]. A list of these different publications ordered according to these citations can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
There is a need for a drill that can be used to rapidly penetrate concrete walls while using minimum tool weight, size and power. In addition, there is a need for effective drills in interplanetary missions such as the Phoenix and MSL (Mars Science Laboratory) missions. In the Phoenix and MSL missions, a Phoenix Mars lander or surface rover targets a region using a robotic arm to dig and analyze the target environment including the geology and geochemistry of the region. Further, in-situ exploration missions (e.g., for NASA) increasingly require analysis of acquired samples to detect and characterize the presence of potential biomarkers of life and water, as well as determine the geological properties. For these missions, there is a critical need to produce samples using effective mechanisms. These problems may be better understood with a description of prior art drilling systems.
For planetary applications, prior art systems provided an ultrasonic/sonic driller/corer (USDC) [Bao, et al., 2003; Bar-Cohen et al., 1999; NDEAA Website] that addressed the need: (1) to use low axial forces and holding torques; (2) for lightweight hardware; and (3) for a drill that consumes low power with the ability to efficiently duty cycle the used power. To enhance the capability of the USDC, sensors were mounted on the USDC and allowed to conduct real-time measurements inside the drilled borehole [Bar-Cohen et al., 2005]. Following the development of USDC, additional designs were developed as disclosed in [Aldrich et al., 2006; Badescu et al., 2007; Bar-Cohen et al., 2002; Bar-Cohen et al., 2003; Bar-Cohen and Sherrit, 2003; Bar-Cohen et al., 2005a; Bar-Cohen et al., 2005b; Bar-Cohen et al., 2007; Sherrit et al., 2001; Sherrit et al., 2002; Sherrit et al., 2003].
FIG. 1 illustrates a photographic view of a USDC showing its ability to drill with minimum axial force (left), and a schematic diagram of its cross-section (right). As illustrated in FIG. 1, the USDC is a drill that consists of three key components: (1) an actuator (also called transducer); (2) a free-mass; and (3) a bit.
The actuator operates as an vibratory hammering mechanism that drives the free-mass into the bit creating stress pulses that fracture the rock or concrete that is in contact with the bit. The actuator consists of a stack of piezoelectric rings with backing for forward power delivery and a horn for amplification of the induced displacement. The USDC is actuated by a piezoelectric stack that is driven in resonance and is held in compression by a stress bolt that prevents its fracture during operation (the piezoelectric rings are made of ceramic that can break if subject to tension). In the basic design, the piezoelectric stack has a resonance frequency of about 20-kHz but drills with frequencies ranging from 5 to 30 kHz. The actuator drives a free-flying mass (free-mass), which bounces between the horn tip and the bit converting the mechanical impacts to hammering at sonic frequencies. The impacts of the free-mass create stress pulses that propagate to the interface of the bit and the material onto which the USDC is placed in contact. The drilled rock or concrete is fractured when its ultimate strain is exceeded at the rock/bit interface.
However, the above design does not perform rotary hammering in a manner that can be commercialized for the construction and remodeling industries. In this regard, while the prior art USDC may be useful and novel, it cannot be utilized with commercial products. Thus, prior art drills fail to provide an effective large diameter drill that performs high speed drilling and that also enhances the capability of commercial rotary drills. Also, there is a need to address the challenges that are inherent to other drills that include large mass and requirements of a high axial preload or weight on bit.
Accordingly, what is needed is an effective large diameter drill that performs high speed drilling, can be used with commercial rotary drills, and that include large mass and a high preload or weight on the drill bit.